# split phase power

Discussion in 'General Electronics Chat' started by shmerd, Oct 28, 2004.

1. ### shmerd Thread Starter New Member

Oct 28, 2004
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I would love to find a clear explanation. Is the power coming into my house single phase(2 110 lines in phase with each other)? split phase (2 110 line 180 out of phase)? If B, why is it refered to as single phase? I believe it is B or the two legs of 220 would read 0 volts? If someone could get back to me I would appreciate it! If there is a good online resource please let me know. This website calls split phase, single phase without giving any explanation.

2. ### Perion Active Member

Oct 12, 2004
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Confusion can exist because of our definitions. Your home's incomming power is both split phase and single phase. They aren't mutually exclusive types. There a pretty good explanation with good diagrams here at http://www.allaboutcircuits.com/vol_2/chpt_10/1.html

In the summary it says:
Even this could be a bit confusing because of the statement about split phase having "both voltage waveforms in phase, or in step, with each other". Refer to the diagram below.

If you connected a dual trace oscope's probes' gnds to the Neutral (center tapped wire) and put one probe on phase A and the other on phase B the waveforms would be 180 degrees out of phase. When A peaks positive B peaks negative. So how is it that the A-Neutral and B-Neutral voltages are said to be "in phase"? [Of course, it makes no sense to ask about the phasing of A-B - any voltage is always in phase with itself.]

The author explains that instead of supplying your house from the grounded center tapped transformer ("split phase") secondary you could substitue two series connected 120 vac single phase generators (synchronized and in phase ) and ground their tie point and have exactly the same system. They must be sychronized in phase since if they were otherwise their voltages would buck or cancel (a little like connecting batteries in series but opposite directions). Yet, if you choose the tie point (where gen 1 connects to gen2) as a measurement reference for your oscope, the other two leads supplying phases A and B in your panel would display waveforms 180 degrees out of phase, just like before. This out of phase characteristic is nothing more than the result of your choice of reference for the waveforms - you are measuring "from" the mid-point "out toward" the two opposite polarities of the winding.

The bottom line is this: electrically speaking (vs. some arbitray place we may choose for a measurement reference) the voltages across the two secondary portions are in phase. They don't buck or cancel but are series aiding - their voltages add directly with no phase angle to contend with. This is just the result of tapping a single winding right in its center point. Nothing mysterious happens. So you have a single phase (vs. some other multi-phase system like a closed delta three phase, etc.), split phase system (the secondary single phase winding is split in two, but still connected, parts by center tapping it).

Perion

Oct 28, 2004
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May 21, 2005
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